Under this very wrong way to throw that out there you realize that ZERO coaches in this country in FBS football get anywhere near an A...

http://www.coacheshotseat.com/WinningestActiveCoachesIA.htm

Only 7 would get a B. And below are your other career C coaches in that same category...

0.773 Rod Carey Northern Illinois
0.751 Nick Saban Alabama
0.748 Craig Bohl Wyoming
0.744 Brian Kelly Notre Dame
0.743 Hugh Freeze Mississippi
0.742 Mark Richt Georgia
0.735 Gary Patterson TCU
0.734 Chris Creighton E. Michigan
0.733 Bobby Petrino Louisville
0.733 Les Miles  LSU
0.731 Bobby Wilder Old Dominion
0.730 Bo Pelini Nebraska
0.730 Steve Spurrier South Carolina
0.729 David Shaw Stanford
0.727 Mark Hudspeth La. Lafayette
0.706 Jim Mora UCLA

In a scenario like this even in a school setting they would apply a bell shaped curve to make sure to provide an A to the current highest scorer. Typically when curved the top 10-15% will be adjusted to be in the A category. Then 10-15% for the B category - this will bring Bronco in as a solid B...but even then it is a very dumb way to try to associate a winning percentage in sports....

Would you say that Jose Altuve, (HOU) .341 AL batting champ received an F for his batting on the season?

http://www.k12academics.com/education-assessment-evaluation/bell-curve-grading#.VEVyZfnF8pk
http://en.wikipedia.org/wiki/Grading_on_a_curve